Computer for aircraft load distribution



COMPUTER, FOR AIRCRAFT LOAD DISTRIBUTION Filed Jan. 1, 1944 2 Sheets-Sheet l WILL/AM FRIEDMAN ERNEST w. SCHL/EBEN INVENTORS" Dec. 19, 1944. E. w. SCHLIEBEN ETAL 2,365,494-

COMPUTER FOR AIRCRAFT LOAD DISTRIBUTION Filed Jan. 1, 1944 2 Sheets-Sheet 2 W/LL/AM FRIEDMAN ERNEST w. SCHLIEBEN INVENTORS BY zz zi shall, however, be in no way limitative Patented Dec. 19, 1944 UNITED STATES PATENT orrlce COMPUTER FOB AIRCRAFTLOAD DISTRIBUTION Ernest w. Schlleben, Scarsdale, and wmnm Friedman, New York, N. Y., aasirnors to York Research Corporation, New York, N. Y.

Application January 1, 1944, Serial No. 516,628

Claims. 01. 235-41) This invention relates in general to an instrument for determining the position of the center of gravity in a loaded vehicle, and more particularly to a computing instrument for the determination of the horizontal position of the center of gravity of a. loaded aircraft, giving at the same time an indication of the total weight of the load.

When loading an aircraft, it is of importance to enable the pilot and/or the freight handler at anytime before the take-off to determine as quickly and accurately as possible the horizontal position of the center of gravity of the loaded craft. Means known for this purpose are generally complicated and require detailed tabulated data in which serious errors are sometimes not easily recognized.

The main object of the present invention is to provide for an instrument by means of which the horizontal position of the center of gravity of an aircraft can easily be established;

Another object of the invention is to provide for an instrument for the determination in an aircraft of the horizontal position of the center of gravity as well as of the total weight as soon as the location and magnitude of single weights or load reactions are'known;

A further object of the invention is to render such an instrument simple and cheap in construction and easy to operate;

A still further object of the invention is to make the instrument compact in construction so that it takes up as little space as possible;

A further object of the invention is to create acomputing instrument for the determination of the horizontal position of the center of gravity of an aircraft which is entirely independent of other parts of the aircraft and can easily be used at whichever place it is convenient.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawings which but merely illustrative.

In the drawings:

Fig. 1 shows the line arrangement on the chart of a computing instrument according to the invention;

Fig: 2 shows one of the indicators with a runner as used in connection with the chart in Fig. 1;

Fig. 3 shows an embodiment of an assembled computer with the indicators set in two different positions to illustrate the operation of the instrument.

In using the computing instrument described mechanical, electrical, hydraulic, pneumatic, or

any other known means to suitable indicating instruments inside the craft, or spring means, pressure gauges or the like may be employed to determine the wanted magnitudes from outside the craft.

In Fig. 1 of the drawings only the line arrangement of the computer chart is shown without any movable parts for the operation of the instrument, in order togive a clear picture of the lines themselves. will be explained hereafter in connection with Fig. 3 of the drawings.

Referring now to Fig. 1, the chart shown contains two coordinate lines II and I2 formed each as an are about center points l3 and I4 respectively. Both coordinate lines have calibrations representing values proportional to the loads or pressures in the supporting members of an air craft. As indicated in the example shown in the drawings, the coordinate line I I represents values between 300 and 700 pounds per square inch forthe main wheels while the coordinate line 1! represents values between zero and 500 pounds per square inch for the nose or tail wheels. These values are, in the embodiment shown, pressures in the shock struts of the supporting members but they could as well be indicated as actual weights. The two coordinate lines H and I2 are shown in such relative position that they intersect at .a point l5 which results in a convenient shape of the chart and arrangement of the movable indicators as will be shown later on. The outline of the chart is indicated at 16, but the ends of the chart have been broken away in Fig. 1. The entire shape of the chart itself suitable for the chosen line arrangement is shown on the right side 'of Fig. 3.

A family of lines I! is shown in the space between the coordinate lines I l and [2. These are lines of equal total loads as plottedirom the indications on the coordinate lines II and 12. Each intersection of radii drawn from the center points l3 and H to values on the coordinate lines It and I2 respectively represents a value of the The operation of the instrument total load on all wheels of the aircraft and the points of equal total loads are interconnected to form the load lines IT as shown for loads from 11,000 to 21,000 pounds. It may be pointed out in this connection that the calibrations on the coordinate lines H and 12 indicate pressures or loads on the individual wheels or supporting members. Therefore, when two wheels are concerned, the value on the associated coordinate line, through which a radius has to be drawn as mentioned before, represents the mean pressure cr load on the two individual wheels and must be doubled in order to give the total pressure or load on both wheels which is needed for the computation of the points of the load lines l1.

Another family of lines i8, intersecting lines 11, may be called longitudinal load distribution lines as they give an indication for the pomtion of the center of gravity in the direction of the longitudinal axis of the aircraft. Such position ma be given either in terms of distance from a fixed point, e. g. the nose of the aircraft or, as more usual. in terms of percent of the mean aerodynamic chord (MAC) the latter designation has been used in the drawings. Longitudinal load distribution lines from 22%% to 45% MAC are shown in Fig. 1. Each of these lines is a line of equal horizontal distances X of the center of gravity from a chosen fixed point according to the formula P1 and P: in this fcrmLla are the total weights on the nose (or tail) and main wheels respectively; a and b are the horizontal distances of these wheels from the chosen fixed point. If P1 and P2 are the pressures or loads indicated in the shock struts of an aircraft, these values have to be corrected for that portion of the weight of the landing 8 which lies beneath the points of the supporting members at which the pressures are determined. For each value of P1 and P: the radii drawn through these values from the center points l3 and I4 intersect in a point of the longitudinal load distribution lines IS. The lines are formed by interconnecting points of equal longitudinal distances.

In Fig. 1 some parts of the area covered by the families of lines I! and I! have been shaded. This shading indicates danger-zones." The iongitudinal center of gravity position for instance is according to Fig. 1 considered as safe for the operation of the aircraft as long as it lies in any area between the 25% and the 40% lines, while the operation of the aircraft would not be safe with the longitudinal position of the center of gravity outside these lines. The maximum safe total weight according to the shading in Fig. 1 is 20,000 pounds.

The computer accordingto the invention contains another family of lines which represent moments as means of indicating the lateral position of the center of gravity of the aircraft. Before, however, these lines can be described, it is necessary to explain another group of lines which serve for the construction of the "moment lines."

On the lowerxright side of the chart in Fig. 1, two curves l and 20 are shown. Both curves are equal to each other and symmetrical about a radius drawn from point I4 through the intersection point 2| of the curves l9 and 20. Point 2! is in this case located on an are which forms the continuation of the coordinate line II. The curves II and zllareplottedsothattbemgularmovement of a line going through the center point II and the intersection II and rotating around point H is for each chosen point on the curves l0 and 20 proportional to a certain amount of pressure difference between the two nose or tail wheels. The angular position of the line through point I4 is therefore an indication for the pressure difference or the moment between the two nose or tail wheels. Curve II is thereby, as indicated by L R to be used when the load on the left hand wheel is larger than on the right hand wheel, while curve 20, as indicated by R L is to be used when the load on. the right hand wheel is larger than the one on the left hand wheel.

Another pair of similar curves 22 and 23 intersecting at a point 24 is plotted on the lower left side of the chart in Fig. 1. These curves are exactly the same as curves I I and 20 with the difference that they are associated with the load differences or the moments on the main wheels and plotted symmetrically to a line going through the intersection point 24 and the center point it and rotating around the latter point.

The aforementioned family of "moment lines 25 is plotted in the lower center of the chart. Each line is the connection of points of equal total moments as received from the single moments on the main and nose or tall wheels respectively. Such total moments are indicated through the intersections of radii through the center points I! and II and the points found on the curves I! or 20 and 22 or II respectively. These latter points are found as points of angular movements of lines -21 and |824 respectively (not shown in Fig. 1), proportional to pressure differences on the associated wheels as read from the indications on the coordinate lines H and 12. According to the position of the moment on either side of the longitudinal axis of the aircraft, either the curves L R or R L" are used for this purpose. The readings on the hydraulic or similar instruments mentioned above, which show the pressures at the individual reaction points, are the indications for the left or right hand location of each individual moment.

In Fig. 1 moment lines are drawn for values from. zero to 300,000 inch pounds on left and right side and shadings outside of the lines designated by "200,000" indicate that for safe operation of the aircraft the total moment should not exceed the aforementioned value. If the actual lateral position of the center of gravity is wanted as distance from the longitudinal axis of the aircraft, the moment read from lines II has to be divided by the total weight of the loaded aircraft as read from the load lines H.

In orderto take into accolmt different velocities of side wind which obviouslyinfluences the magnitude of the moments, a set ofcurvesil and 2'! similar to the curves 2! and I! is employed which are symmetrically located on both sides of the curves- 2! and 23. These curves are designated by "L, "L and L and by 20R, R and R respectively, indicating so many miles per hour of a side wind comingfromtbeleftorrightsidsrespeetivelyoftheaircrsft. lfsuchwindsprevail these curvesare used instead of curves and II for the determination of the moment themain wheels.

For the operation of tin computer. two equal indicators are used which are rotatably tothechartatlland llbutnot indicator has a central or zero hairline 28 going through the hinge point 29 around which the indicator rotates when assembled with the chart.

Three other radial hairlines 23a are shownformlongitudinal position of the center of gravity and of the total weight in case of head or tail wind.

The end 3| of the indicator, opposite its hinge end, is somewhat narrower than the rest of the "indicator and forms a guide for a runnerv 32 which is adapted to slide radially along the nar.

row end of the indicator. The runner is calibrated with two hairlines 33 which intersect in a point 34 on the zero hair line 28 and form equal angles with the latter hair line.

While the chart itself may be made out of any suitable material, the indicators and the runners, if designed as shown in the drawings must be made out of transparent, e. g. plastic material to enable the reading of all hair lines against the chart.

The operation of the computer according to the invention can best be explained from Fig. 3 which is an assembly of the chart with the two indicators and shows the indicators in two different positions to which they have to be set in order to determine the horizontal position of the center of gravity of a loaded aircraft. The computation shown and hereafter described relates to a land aircraft with two main and two nose wheels but, as will be shown later on, the computer can as well be used and a similar procedure followed for an aircraft with only three supporting members. Of course any other kind of load reactions may be used to enable the use of the computer.

In Fig. 3 the same reference numbers have been employed as in Figs. 1 and 2. Only the reference numbers for the parts of the second indicator have been distinguished by the addition of the letter a as only one of the indicators has, been shown in the previous views. Some of the designations and the shading have'been omitted in Fig. 3 to make the drawings easier understandable. For the same reason the wind hair lines have been omitted on the indicators and only the zero hair line has been shown, also the wind curves 26 and 21 from Fig. 1 have been omitted in Fig. 3.

In the example illustrated in Fig. 3 it has been assumed that the indicating instruments associated with the different shock struts show pressures per square inch of 410 and 490 pounds respectively on the two main wheels, and of 270 and 330 pounds respectively on the two nose wheels ofthe four wheeled aircraft .under consideration. The average pressure per square inch on each main wheel is therefore 450 pounds, the average pressure on each nose wheel is 300 pounds. The indicators 3| and 3m which are shown in phantom lines. in Fig. 3 are set so that their zero hair lines 28 and 28a (shown in full) cross the values 450 and 300 of the coordinate lines H and I2 respectively. The runners on these indicators are set so that their hair lines 33 and 33a (shown in full) cross the .values 410 and 490 on coordinate line II and the values 270 V gives a reading of 16,000 pounds when read 76 against the load lines l1, and a reading of 2896 MAC when read against the longitudinal load distribution lines it.

The indicators are now-rotated (without moving the runners with respect to the indicators) until theintersections 34 and 34a of the runner hair lines fall on curves 22 and I8 respectively.

In this case it has been assumed that at the main wheels as well as at the nose wheels the larger load is on the left side of the longitudinal axis of the aircraft. Would the larger load on the main wheels for instance be on the right side,

then curve 23 would have to be used instead of curve 22. v

The indicators 3! and 31a as well as the different hair lines are shown in their second positions with broken lines. Their zero hair lines intersect at a point 36 which indicates a moment ofl00,000 inch pounds to the leftwhen read against the moment lines 25. The actual transverse center of gravity position can be found in inches from the center line of the aircraft by dividing the moment by the weight If the instrument is to be used for an aircraft with only three supporting members the runner 32 (not shown in Fig. 3) on the indicator 3la would have to be set so that the intersection 34a of the hair lines 33a coincides with the coordinate line l2. In this case the zero hair line 28a would run through the intersection 2| of the main the same whether the aircraft for which the computer shall be used has main and nose wheels or main and tail wheels. Therefore wherever the term nose wheels or tail wheels is used within this application both terms have to be considered asequivalent and can be replaced by each other. Furthermore, the term ground ed used in the claims should be understood in its broadest sense, meaning as well grounded on land as on water.

What we claim is:

1. In an instrument for the determination of the horizontal position of the center of gravity of an aircraft by-means of load reactions caused by the weight of the grounded aircraft: a chart having two coordinate lines, each of said coordinate lines forming a circular arc around adifferent center point and being calibrated according to values indicating the magnitude of said load reactions; two movable indicators on said chart, each associated with a different one [of said coordinate lines and adapted to rotate around the center point of its associated coordinate line and having an indicating line radially extending along each indicator, said indicating lines intersecting at each position of said indicators within the range of operation of the instrument; a runner on at least one of said indicators, said runner being adapted to slide radially on said indicator and having two intersecting hair lines, said hair lines being so arranged that the angle between them would be bisected by a line passing through their intersection and the center point of the indicator on which said runner slides; a family of lines on an area of the chart over which the intersections oi said indicating lines move when the indicators are operated, each line of said family representing points of equal longitudinal positions of the center of gravity of the aircraft as determined by the intersections of said indicating lines when set according to the given load reactions on said two coordinate lines; a second family of lines on said same area of the chart, each line of said second family representing values of the moments around the longitudinal axis of said aircraft as caused by said load reactions, said moments being determined by the intersections of said indicating lines when said indicators are set in accordance with the values of said load reactions, the setting of the indicators being determined by two pairs of curves on said chart within the operating area of said indicators, each pair of curves being associated with a different one of said indicators and enabling a setting of said indicators so that the angle between each indicating line and a reference line is always proportional to the difference between the values on the associated coordinate line to which the hair lines on said runners had been set.

2. An instrument as claimed in claim 1, said area of the-chart over which the intersections of the indicating lines move, the lines of said third family representing each points of equal total weights as determined by the intersections of said indicating lines when said lines are set accordin: to the load reactions given on said two coordinate lines.

3. An instrument as claimed in claim 1, said instrument having a number of further pairs of curves similar to those claimed in claim 1 and arranged symmetrically to both sides of one of said pairs of curves claimed in claim 1, said further "pairs of curves representing lines to which the indicators can be set for the determination oi said moment when side wind on the aircraft has to be taken into account.

4. An-indicating instrument as claimed in claim l,.said indicating instrument having on-said indicators besides said indicating line claimed in claim 1 at least one further radially extending indicating line, said further indicating lines representing wind lines which are used for the determination of the longitudinal position of the center of gravity and of the total weight when wind in longitudinal direction is aiiecting the balance of the aircraft.

' 5. A computer for the determination of the horizontal position of the center of gravity of an aircraft from the known load reactions in four I instrument having a third family of lines on an of said runners having two intersecting hair lines,

two families of lines on said chart within the area of the intersections of said indicating lines. said families of lines being indications for the longitudinalandthelateralpositlonofthecenterof gravity respectively of the aircraft, and two pairs oi'curvesonsaid chartwithintheoperatingarea ofsaidindicators,eachoneofsaidpairs ofcurves being associated with a different one of said indicators and enabling a etting of said indicators Proportional to the differences between the load reactions indicated on the respective coordinate lines.

ERNEST W. BCHLIEBEN. 

